(1) Field of the Invention
This invention relates to a flow-rate control valve, and more particularly to a flow rate control valve having a quick discharge valve.
(2) Description of the Prior Art
In an actuator, fluid pressure is applied to a piston which is slidingly fitted in a cylinder, so that the piston is displaced within the cylinder and the displacement of the piston is derived as useful work through the medium of a rod secured to the piston. In this case, the output of the cylinder is dependent on the pressure (in general, pressure in a headside chamber in the cylinder with respect to the piston) applied to the piston for the desired work. The pressure required for returning the piston to its initial position (pressure on the rod-side chamber in the cylinder) should not necessarily be the same as that required for performing the work, i.e., it should be minimized to effect a piston return to its initial position. However, it has been the general practice that, after a pressure has been adjusted by means of a pressure regulating valve, a pressure at the same pressure level is applied to the head-side and rod-side chambers in the cylinder via a direction changeover valve, so that energy is wasted in returning the piston to its initial position, i.e., on its return stroke.
It is an object of the present invention to provide a flow rate control valve having a quick discharge valve, in which a working pressure is quickly applied to a cylinder so as to drive the cylinder on the advance stroke of a piston, and to quickly discharge pressure therefrom when pressure is to be discharged from the cylinder on its return stroke.